U.S. patent application number 13/271550 was filed with the patent office on 2012-04-12 for p/s-tm-comprising zeolites for decomposition of n2o.
This patent application is currently assigned to BASF SE. Invention is credited to Stephan Deuerlein, Tobias Rosendahl.
Application Number | 20120087851 13/271550 |
Document ID | / |
Family ID | 45925295 |
Filed Date | 2012-04-12 |
United States Patent
Application |
20120087851 |
Kind Code |
A1 |
Deuerlein; Stephan ; et
al. |
April 12, 2012 |
P/S-TM-COMPRISING ZEOLITES FOR DECOMPOSITION OF N2O
Abstract
The present invention relates to the use of a zeolite catalyst
comprising at least one transition metal and in addition sulfur
and/or phosphorus atoms for reducing the content of nitrogen oxides
in a gas, and also to a process for reducing the content of
nitrogen oxides in a gas by bringing this gas into contact with
such a zeolite catalyst.
Inventors: |
Deuerlein; Stephan;
(Ludwigshafen, DE) ; Rosendahl; Tobias; (Mannheim,
DE) |
Assignee: |
BASF SE
Ludwigshafen
DE
|
Family ID: |
45925295 |
Appl. No.: |
13/271550 |
Filed: |
October 12, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61392049 |
Oct 12, 2010 |
|
|
|
Current U.S.
Class: |
423/239.2 |
Current CPC
Class: |
B01D 2257/404 20130101;
B01D 2255/50 20130101; B01D 2251/206 20130101; B01D 2255/20753
20130101; Y02P 20/51 20151101; C07C 51/42 20130101; Y02P 20/153
20151101; Y02P 20/328 20151101; B01D 2255/20738 20130101; B01D
2255/20746 20130101; Y02P 20/30 20151101; Y02P 20/50 20151101; B01D
2251/208 20130101; B01D 2258/0283 20130101; B01D 2257/402 20130101;
B01D 2251/202 20130101; B01D 53/9413 20130101; B01D 2255/207
20130101; Y02P 20/151 20151101; B01D 2251/204 20130101; B01D
2255/20761 20130101; B01D 2251/506 20130101; B01D 53/8628 20130101;
Y02C 20/10 20130101; C07C 51/42 20130101; C07C 55/14 20130101 |
Class at
Publication: |
423/239.2 |
International
Class: |
B01D 53/56 20060101
B01D053/56 |
Claims
1-13. (canceled)
14. A process for reducing the content of nitrogen oxides in a gas
comprising contacting said gas with a zeolite catalyst comprising
at least one transition metal and sulfur and/or phosphorus
atoms.
15. The process of claim 14, wherein said at least one transition
metal is selected from the fourth period and/or groups 8 to 11 of
the Periodic Table of the Elements.
16. The process of claim 14, wherein said at least one transition
metal is selected from the group consisting of Sc, Ti, V, Cr, Mn,
Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au, and mixtures
thereof.
17. The process of claim 14, wherein said at least one transition
metal is present in said zeolite catalyst in a concentration of
from 0.1 to 10.0% by weight, based on the total weight of said
zeolite catalyst.
18. The process of claim 14, wherein said sulfur and/or phosphorus
atoms are present in said zeolite catalyst in a concentration of
less than 10% by weight, based on the total weight of said zeolite
catalyst.
19. The process of claim 14, wherein the zeolite of said zeolite
catalyst is selected from the group consisting of BEA, FAU, FER,
MFI, and mixtures thereof.
20. The process of claim 14, wherein said at least one transition
metal is Fe, Cu, Co, and/or Ni.
21. The process of claim 14, wherein said method is used in nitric
acid production, in adipic acid production, for power station
offgases, for gas turbines, or for automobile catalysts in the
low-temperature range.
22. The process of claim 14, wherein said process further comprises
contacting said gas with at least one reducing agent.
23. The process of claim 14, wherein said process is carried out at
a temperature of less than 400.degree. C.
24. The process of claim 14, wherein the GHSV is in the range of
from 200 to 200,000 standard lgas/lcath.
25. The process of claim 22, wherein said at least one reducing
agent is selected from the group consisting of nitrogen compounds,
hydrocarbons, CO, SO.sub.2, H.sub.2, and mixtures thereof.
26. The method of claim 18, wherein said sulfur and/or phosphorus
atoms are present in said zeolite catalyst in a concentration of
less than 3% by weight, based on the total weight of said zeolite
catalyst.
27. The method of claim 18, wherein said sulfur and/or phosphorus
atoms are present in said zeolite catalyst in a concentration in
the range of from 0.2 to 2.0% by weight, based on the total weight
of said zeolite catalyst.
28. The process of claim 24, wherein the GHSV is in the range of
from 5000 to 50 000 standard lgas/lcath.
29. The process of claim 24, wherein the GHSV is in the range of
from from 10 000 to 30 000 standard lgas/lcath.
Description
[0001] The present invention relates to the use of a zeolite
catalyst comprising at least one transition metal and in addition
sulfur and/or phosphorus atoms for reducing the content of nitrogen
oxides in a gas, and also to a process for reducing the content of
nitrogen oxides in a gas by bringing this gas into contact with
such a zeolite catalyst.
[0002] The use of metal-doped catalysts in processes for the
catalytic removal of nitrogen oxides is known from the prior
art.
[0003] DE 101 12 396 A1 discloses a process for reducing the
content of N.sub.2O in gases. Here, a selected zeolite catalyst is
used. This is present in the H form and/or comprises exchanged iron
and is characterized by the presence of nonlattice aluminum in
addition to the lattice aluminum in a molar ratio of from 1:2 to
20:1. Furthermore, this document discloses that dealumination or
demetallation can be carried out by means of a mineral acid
treatment. This is carried out using acids selected from among HCl,
HF, H.sub.2SO.sub.4, HNO.sub.3 and H.sub.3PO.sub.4. The acid
treatment as described in DE 101 12 396 A1 is not carried out to
introduce sulfur and/or phosphorus atoms onto the catalyst. No
content of sulfur and/or phosphorus atoms in the finished catalyst
is disclosed in this document.
[0004] WO 03/084646 A1 discloses a process for reducing the content
of NO.sub.x and N.sub.2O in gases, in particular in process gases
and offgases, which comprises addition of at least one
nitrogen-comprising reducing agent to the NO.sub.x- and
N.sub.2O-comprising gas in an amount not less than that required
for complete reduction of the NO.sub.x, addition of a hydrocarbon,
carbon monoxide, hydrogen or a mixture of one or more of these
gases to the NO.sub.x- and N.sub.2O-comprising gas to reduce the
N.sub.2O and introduction of the gas mixture into at least one
reaction zone which has temperatures of up to 450.degree. C. and
comprises one or more iron-laden zeolites. According to this
process, catalysts which are based on zeolites into which iron has
been introduced by means of solid-state ion exchange are used. For
this purpose, commercially available ammonium zeolites are usually
treated with appropriate iron salts, e.g. FeSO.sub.4.7 H.sub.2O.
After calcination, the iron-comprising zeolites are thoroughly
washed in distilled water, filtered off and dried. Thus, the
document cited discloses zeolite catalysts which are doped with
iron. However, the sulfate anions which are likewise applied
together with the iron cations are removed again by means of the
thorough washing, so that no sulfur is present on the iron-doped
catalyst.
[0005] DE 102 15 605 A1 likewise discloses a process for reducing
the content of NO.sub.x and N.sub.2O in gases, in particular in
process gases and offgases, where the gas to be treated is brought
into contact with a catalyst which is based on a zeolite and is
doped with iron. According to this document, the doping with iron
can likewise be achieved by applying FeSO.sub.4.7 H.sub.2O to the
zeolite. Moreover, here too, the sulfate anions are removed again
by thorough washing, so that no sulfur and/or phosphorus atoms are
present In the final catalyst.
[0006] DE 10 2005 022 650 A1 also discloses a process for reducing
the content of nitrogen oxides in gases. For this purpose, the gas
to be treated is brought into contact with a zeolite which is doped
with copper and/or iron atoms. The presence of sulfur or phosphorus
atoms on the zeolite catalyst is likewise not disclosed in this
document.
[0007] The catalysts known from the prior art, in particular the
iron-doped zeolites, have an activity for the degradation of
nitrogen oxides in gases which is still capable of improvement.
Furthermore, there is a need for an improved zeolite catalyst which
has the same activity as the systems known from the prior art even
at low temperatures, or displays a correspondingly higher activity
at the same temperature. A catalyst which displays a sufficiently
high activity even at a relatively low reaction temperature would
be advantageous because the offgas from many industrial plants has
a low temperature and heating of this offgas before reaction over
the appropriate catalyst is unattractive for ecological and
economic reasons.
[0008] The objects mentioned in the light of the available prior
art are achieved, according to the invention, by the use of a
zeolite catalyst for reducing the content of nitrogen oxides in a
gas, where the zeolite catalyst comprises at least one transition
metal and in addition sulfur and/or phosphorus atoms.
[0009] The objects are also achieved by a process for reducing the
content of nitrogen oxides in a gas by bringing the gas into
contact with a zeolite catalyst as defined above.
[0010] The zeolite catalyst used according to the invention will be
described in detail below:
[0011] The basis of the zeolite catalyst used according to the
invention is a zeolite. Zeolites are known per se to those skilled
in the art and are disclosed, for example, in Catalysis and
Zeolites, Fundamentals and Applications, J. Weitkamp, I. Puppe,
(eds), Springer-Verlag, Berlin, Heidelberg 1990.
[0012] In general, all zeolites known to those skilled in the art
are suitable for the zeolite catalyst used according to the
invention. These are named in the following using the three letter
nomenclature of the IZA (international zeolite association)
structure commission known to those skilled in the art.
[0013] Zeolites which are particularly suitable for the purposes of
the invention are selected from the group consisting of BEA, CHA,
FAU, FER and MFI and mixtures thereof.
[0014] According to the invention, the zeolite catalyst comprises
at least one transition metal. The term transition metal is known
per se to those skilled in the art and describes the group of
elements in transition groups 3 to 12 of the Periodic Table of the
Elements (new IUPAC nomenclature).
[0015] In a preferred embodiment, the catalyst used according to
the invention comprises at least one transition metal selected from
the fourth period and/or groups 8 to 11 of the Periodic Table of
the Elements.
[0016] The present invention therefore relates particularly to the
use according to the invention where the at least one transition
metal is selected from the fourth period and/or groups 8 to 11 of
the Periodic Table of the Elements.
[0017] The catalyst used according to the invention more preferably
comprises at least one transition metal selected from the group
consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd,
Ag, Os, Ir, Pt, Au and mixtures thereof.
[0018] The present invention therefore relates particularly to the
use according to the invention where the at least one transition
metal is selected from the group consisting of Sc, Ti, V, Cr, Mn,
Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au and mixtures
thereof.
[0019] In a particularly preferred embodiment, the catalyst used
according to the invention comprises Fe, Cu, Co and/or Ni, very
particularly preferably Fe, as at least one transition metal.
[0020] The present invention therefore very particularly preferably
relates to the use according to the invention where the at least
one transition metal is Fe, Cu, Co and/or Ni.
[0021] Examples according to the invention of nitrogen oxides are
preferably selected from the group consisting of dinitrogen
monoxide N.sub.2O, nitrogen oxides NO.sub.x, where x is 1 or 2, and
mixtures thereof. In a preferred embodiment, the gas to be treated
comprises a little (NO.sub.x/N.sub.2O<0.5) and in particular no
nitrogen oxides NO.sub.x. In a preferred embodiment, a stage for
decreasing the amount of NO.sub.x therefore precedes the use
according to the invention. Methods of decreasing the amount of
NO.sub.x are known to those skilled in the art.
[0022] The content of the nitrogen oxide N.sub.2O is particularly
preferably reduced by means of the use according to the
invention.
[0023] The at least one transition metal which is present according
to the invention can generally be comprised in the zeolite catalyst
used according to the invention in any amount which gives the
catalyst used according to the invention a particularly high
activity, for example in the degradation of nitrogen oxides, in
particular dinitrogen monoxide N.sub.2O.
[0024] In a preferred embodiment, the at least one transition metal
is present in the catalyst used according to the invention in a
concentration of from 0.1 to 10.0% by weight, particularly
preferably from 0.25 to 5.0% by weight, very particularly
preferably from 0.5 to 2.5% by weight, for example 0.7 or 2.5% by
weight, in each case based on the total zeolite catalyst.
[0025] In a preferred embodiment, the present invention therefore
relates to the use according to the invention where the at least
one transition metal is present in a concentration of from 0.1 to
10.0% by weight, particularly preferably from 0.25 to 5.0% by
weight, very particularly preferably from 0.5 to 2.5% by weight,
for example 0.7 or 2.5% by weight, in each case based on the total
zeolite catalyst.
[0026] The at least one transition metal which is present according
to the invention can be present in either cationic or elemental
form in the zeolite catalyst used according to the invention. If
the transition metal is present in cationic form, it is preferably
present in oxidation numbers which are typical of the respective
transition metal as a result of its position in the Periodic Table.
In the preferred case of iron being present as transition metal in
the zeolite catalyst used according to the invention, the oxidation
number thereof is preferably +2 or +3. If the at least one
transition metal is present in elemental form, it has the oxidation
number 0. The at least one transition metal can also be present as
a mixture of various oxidation numbers.
[0027] It is possible, according to the invention, for the at least
one transition metal present to be incorporated into the lattice of
the respective zeolite and/or to be present outside this lattice
structure as nonlattice transition metal.
[0028] Furthermore, the zeolite catalyst used according to the
invention additionally comprises sulfur and/or phosphorus
atoms.
[0029] In the zeolite catalyst used according to the invention, the
sulfur and/or phosphorus atoms can generally be present in any
amount which, in combination with the at least one transition metal
present, gives the zeolite catalyst used according to the invention
a particularly high activity in the degradation of nitrogen oxides,
in particular dinitrogen monoxide N.sub.2O.
[0030] In a preferred embodiment, sulfur and/or phosphorus atoms
are present in the catalyst used according to the invention in a
concentration of less than 10% by weight, based on the total
catalyst.
[0031] In a further preferred embodiment, sulfur and/or phosphorus
atoms are present in the catalyst according to the invention in a
concentration of less than 3% by weight, very particularly
preferably from 0.2 to 2.5% by weight, in each case based on the
total catalyst.
[0032] The present invention therefore also preferably provides for
the use according to the invention in which the sulfur and/or
phosphorus atoms are present in a concentration of less than 10% by
weight, preferably less than 3% by weight, particularly preferably
from 0.2 to 2.0% by weight, based on the total catalyst.
[0033] The sulfur and/or phosphorus atoms which are present
according to the invention can be present in a uniform oxidation
state or in combinations of various oxidation states in the zeolite
catalyst used according to the invention. In the embodiment of the
invention in which sulfur is present in the zeolite catalyst
according to the invention, this sulfur is preferably present in
the oxidation state +6 or +2 or a combination of these side by
side, but in particular the oxidation state +6.
[0034] In the embodiment of the invention in which phosphorus is
present in the zeolite catalyst according to the invention, this
phosphorus is preferably present in the oxidation state +5 or +3 or
a combination of these side by side, but in particular the
oxidation state +5.
[0035] Sulfur and/or phosphorus can be incorporated into the
lattice of the respective zeolite, or sulfur and/or phosphorus are
present as atoms, cations or anions outside the lattice of the
zeolite, or sulfur and/or phosphorus are present both in the
lattice and also outside the lattice of the respective zeolite.
[0036] The zeolite catalysts used according to the invention
generally comprise aluminum in cationic form which is present in
the lattice. The zeolite catalyst used according to the invention
can, in a further embodiment, comprise not only the aluminum
cations present in the lattice but also corresponding cations which
are present outside the lattice as nonlattice aluminum cations.
[0037] Steaming of the zeolites, i.e. hydrothermal treatment of the
zeolites by passing steam over them at elevated temperatures, or
else treatment with acids are particularly useful for setting a
preferred ratio of nonlattice aluminum to lattice aluminum. A
combination of various methods can also be employed.
[0038] In a treatment with H.sub.2O vapor and/or acid, as is known
to those skilled in the art, dealumination or, if the zeolite
comprises other metals such as Fe, Ga, etc., in addition to Al,
demetallation, i.e. removal of the aluminum or these metals from
the lattice of the zeolite, takes place. The aluminum or the metals
migrate from their lattice positions into the pores of the zeolite
and remain there as amorphous constituents in oxidic or hydroxidic
form as extralattice metal. The degree of dealumination or
demetallation can be set via the duration of the treatment and the
reagent concentration. Part of the extralattice metal produced can
also be removed from the pores during the treatment. As a result,
the metal content of the catalyst can change.
[0039] The treatment of the zeolite with steam can, for example, be
carried out at temperatures of from 300 to 800.degree. C. for a
period of from 0.5 to 48 hours. The zeolite can be exposed to pure
steam or a mixture of nitrogen and/or air and water vapor having a
proportion of water vapor of from 1 to 100% by weight at total
pressures of up to 100 bar. A carrier gas can optionally be added
to the steam or the water vapor mixture. Suitable carrier gases are
inert under the treatment conditions; examples are N.sub.2, Ar, He,
H.sub.2 or a mixture thereof.
[0040] The zeolites can be dealuminated/demetallated further by
means of an additional mineral acid treatment, optionally in
addition to the steam treatment. The acid treatment can both remove
extralattice metal from the pores and lead to further demetallation
of the lattice. This step can, for example, be carried out in a
batch reactor at temperatures of from 0 to 120.degree. C. at a
lattice/zeolite ratio of from 1 to 100 cm.sup.3/g and acid
concentrations of from 0.001 M to the maximum concentration of the
acid. Examples of acids which can be used for this step are HCl,
HF, H.sub.2SO.sub.4, HNO.sub.3 and H.sub.3PO.sub.4. After the acid
treatment, the zeolite is separated off from the reaction mixture
by conventional methods, e.g. by filtration or centrifugation.
[0041] According to the present invention, amorphous metal oxides
or hydroxides are produced at extralattice sites by the
above-described treatment of the zeolite and it is assumed that
they act as catalytic sites to increase the activity in respect of
the degradation of N.sub.2O.
[0042] The zeolite catalyst used according to the invention can
comprise, in addition to the above-described zeolite, the at least
one transition metal and sulfur and/or phosphorus atoms, further
customary components known to those skilled in the art, for example
binders such as aluminum oxide or silicon oxide and mixtures
thereof.
[0043] The zeolite catalyst used according to the invention can be
used in any form which appears to be suitable to a person skilled
in the art, for example as shaped bodies, e.g. extrudates or
honeycomb bodies, crushed material, particles or powder. In
industry, the zeolite catalyst used according to the invention is
preferably used in the form of shaped bodies, for example having a
particle diameter of from 1 to 10 mm, preferably from 1.5 to 5
mm.
[0044] The catalyst used according to the invention can, for
example, be produced by a process which comprises the following
steps:
[0045] (A) application of the at least one transition metal or a
precursor compound thereof to a zeolite,
[0046] (B) calcination of the zeolite from step (A) to convert, if
applicable, the precursor compound into the at least one transition
metal and to obtain a zeolite comprising the at least one
transition metal,
[0047] (C) application of the sulfur and/or phosphorus atoms or a
precursor compound thereof to the doped zeolite from step (B)
and
[0048] (D) calcination of the zeolite from step (C) to obtain the
catalyst to be used according to the invention.
[0049] The individual steps of the process for producing the
catalyst used according to the invention are described in detail
below:
Step (A)
[0050] Step (A) comprises application of the at least one
transition metal or a precursor compound thereof to a zeolite.
[0051] According to the invention, it is generally possible to use
all zeolites which have been mentioned above. In a preferred
embodiment, zeolites selected from the group consisting of BEA,
FAU, FER, MFI and mixtures thereof are used.
[0052] In a preferred embodiment, precursor compounds of the
abovementioned transition metals, particularly preferably the
metals Fe, Cu, Co, Ni or mixtures thereof, are used for this
purpose.
[0053] Particularly preferred precursor compounds for the
transition metal iron which is very particularly preferably used
are Fe(NO.sub.3).sub.2 and Fe(SO.sub.4).
[0054] Step (A) of the process is particularly preferably carried
out by dissolving a suitable amount of the appropriate precursor
compounds in water or an aqueous solution and impregnating the
appropriate zeolites with this aqueous solution. The aqueous
solutions which are preferably used can, in one embodiment,
comprise water as solvent. In a further embodiment, the aqueous
solutions can comprise not only water but also further, polar and
water-miscible solvents, for example alcohols such as methanol,
ethanol, propanols and mixtures thereof.
[0055] Impregnation of a solid with an aqueous solution is known
per se to those skilled in the art. Impregnation is preferably
carried out by spraying the impregnation solution of the
appropriate transition metal or a precursor compound thereof onto
the zeolite.
[0056] The amount of aqueous impregnation solution or the amount of
transition metal or precursor compound of the at least one
transition metal present in this impregnation solution is set so
that an appropriate amount of transition metal is present on the
zeolite after application to the zeolite and drying and
calcination. Methods of determining the appropriate amounts are
known to those skilled in the art.
[0057] In one embodiment of the process, the water present on the
zeolite after application of the at least one metal according to
step (A) of the process is removed, for example by drying. Methods
of drying a solid are known per se to those skilled in the art, for
example filtration, centrifugation and/or heating. In a preferred
embodiment, drying of the zeolite after process step (A) is
effected by heat treatment at a temperature in the range from, for
example, 10 to 150.degree. C. and a pressure of, for example,
atmospheric pressure or a reduced pressure of, for example, less
than 800 mbar. The transition metal-comprising zeolite which has
preferably been dried in this way is preferably transferred
directly to step (B).
Step (B)
[0058] Step (B) comprises calcination of the zeolite from step (A)
to convert, if applicable, the precursor compound into the at least
one transition metal and to obtain a zeolite comprising the at
least one transition metal.
[0059] Calcination of a solid is known per se to those skilled in
the art. The zeolite which has been doped with metal cations in
step (A) is preferably calcined at a calcination temperature of
from 300 to 700.degree. C., preferably from 400 to 600.degree. C.,
particularly preferably from 450 to 580.degree. C. Calcination can
generally be carried out in any suitable atmosphere. Preference is
given to using an inert atmosphere, for example a nitrogen
atmosphere.
[0060] Calcination is carried out until an appropriately doped
zeolite catalyst is obtained. For example, calcination is carried
out for from 1 to 10 hours, preferably from 3 to 6 hours.
[0061] In step (B) of the process, any water still present from the
impregnation step (A) and/or any water of crystallization present
and/or any organic solvent present is/are firstly removed. In
addition, the precursor compound of the at least one transition
metal which is preferably used is converted into the corresponding
transition metal and/or transition metal oxide and/or the at least
one transition metal is at least partly incorporated into the
lattice structure of the zeolite.
Step (C)
[0062] Step (C) comprises application of the sulfur and/or
phosphorus atoms or a precursor compound thereof to the doped
zeolite from step (B).
[0063] Preference is given to applying at least one precursor
compound of the sulfur and/or phosphorus atoms in step (C) of the
process. Examples of appropriate precursor compounds are selected
from the group consisting of sulfurous acid H.sub.2SO.sub.3,
sulfuric acid H.sub.2SO.sub.4, phosphinic acid H.sub.3PO.sub.2,
phosphonic acid H.sub.3PO.sub.3, phosphoric acid H.sub.3PO.sub.4
and mixtures thereof. Preference is given to sulfuric acid and/or
phosphoric acid.
[0064] In a preferred embodiment, the doped zeolite obtained in
step (B) is impregnated with an aqueous solution of the appropriate
precursor compound. As indicated for step (A), an aqueous solution
comprising water can be used. It is also possible to use an aqueous
solution comprising, in addition to water, a polar, water-soluble
solvent, for example alcohols such as methanol, ethanol, propanols
or mixtures thereof, in step (C). An aqueous solution comprising
water as solvent is preferably used in step (C). Very particular
preference is given to using an aqueous solution of phosphoric acid
or an aqueous solution of sulfuric acid or a mixture of these two
aqueous solutions in step (C).
[0065] Impregnation can be carried out by methods known per se to
those skilled in the art, for example by bringing the zeolite from
step (B) into contact with the abovementioned aqueous solutions in
a stirred reactor or by spraying the solutions onto the
zeolite.
[0066] After impregnation, the impregnated zeolite can be dried by
all methods known to those skilled in the art. Appropriate methods
have been mentioned for step (A) and apply analogously to step
(C).
[0067] In the process, it is preferred that no washing of the
zeolite catalyst takes place during or after step (C) since
otherwise sulfur and/or phosphorus atoms would be removed again,
which is undesirable for the purposes of the invention.
Step (D)
[0068] Step (D) of the process comprises (D) calcination of the
zeolite from step (C) in order to obtain the catalyst used
according to the invention.
[0069] Calcination of a solid is known per se to those skilled in
the art. The zeolite which has been doped with transition metal
cations and sulfur and/or phosphorus atoms in step (D) is
preferably calcined at a calcination temperature of from 300 to
700.degree. C., preferably from 400 to 600.degree. C., particularly
preferably from 450 to 580.degree. C. Calcination can generally be
carried out in any suitable atmosphere. Preference is given to
using an inert atmosphere, for example a nitrogen atmosphere.
[0070] Calcination is carried out until an appropriately doped
zeolite catalyst is obtained. For example, calcination is carried
out for from 1 to 10 hours, preferably from 3 to 6 hours.
[0071] In step (D) of the process, any water still present from the
impregnation step (C) and/or any organic solvent present is/are
firstly removed. In addition, the precursor compound of the sulfur
and/or phosphorus atoms which is preferably used is converted into
the sulfur and/or phosphorus atoms or oxides thereof and/or the
sulfur and/or phosphorus atoms are at least partly incorporated
into the lattice structure of the zeolite and/or form a compound
with the at least one transition metal from step (A).
[0072] The steps (A) and (C) can optionally also be combined. This
can be effected, for example, by the above-described transition
metal solution and the above-described solution comprising sulfur
and/or phosphorus atoms being applied in succession or
simultaneously without intermediate calcination and intermediate
drying. As an alternative, steps (A) and (C) can also be carried
out directly in succession without the intermediate step (B).
[0073] An optional dealumination or demetallation of the zeolite
catalyst to be used according to the invention can be carried out
at any point in the production process mentioned by way of example,
in particular before step (A) and/or before step (C) and/or after
step (D). The dealumination or demetallation of a zeolite is known
in principle to those skilled in the art.
[0074] For example, dealumination or demetallation can be effected
by treatment with H.sub.2O vapor. The degree of dealumination or
demetallation can be set via the duration of the steam treatment.
The treatment of the zeolite with steam can, for example, be
carried out at temperatures of from 300 to 800.degree. C. for a
period of from 0.5 to 48 hours. The zeolite can be exposed to pure
steam or a mixture of nitrogen and/or air and steam having a
proportion of water vapor of from 1 to 100% by weight at total
pressures up to 100 bar. A carrier gas can optionally be added to
the steam or the water vapor mixture. Suitable carrier gases are
inert under the treatment conditions; examples are N.sub.2, Ar, He,
H.sub.2 or a mixture thereof.
[0075] The zeolites can, optionally in addition to the steam
treatment, also be dealuminated/demetallated by means of a mineral
acid treatment. The acid treatment can both remove extralattice
metal from the pores and lead to a further demetallation of the
lattice. This step can, for example, be carried out in a batch
reactor at temperatures of from 0 to 120.degree. C. at an
acid/zeolite ratio of from 1 to 100 cm.sup.3/g and at acid
concentrations of from 0.001 M to the maximum concentration of the
acid. Examples of acids which can be used for this step are HCl,
HF, H.sub.2SO.sub.4, HNO.sub.3 and H.sub.3PO.sub.4. After the acid
treatment, the zeolite is separated from the reaction mixture by
conventional methods, e.g. by filtration or centrifugation.
[0076] After production of the zeolite catalyst to be used
according to the invention is complete, this catalyst can be
converted into a suitable form. This is generally carried out by
processes known to those skilled in the art, for example pressing,
pelletization, sieving, crushing, extrusion. Industrially, the
zeolite catalyst used according to the invention is preferably used
in the form of shaped bodies, e.g. extrudates or honeycomb bodies,
for example having a particle diameter of from 1 to 10 mm,
preferably from 1.5 to 5 mm. As an alternative, the zeolite can be
used as starting material in a suitable form in the production of
the catalyst used according to the invention.
[0077] The use according to the invention can generally be employed
in all applications in which the content of nitrogen oxides in a
gas is to be reduced, In a preferred embodiment, the invention is
used in nitric acid production, in adipic acid production, for
power station offgases, for gas turbines or for automobile
catalysts in the low-temperature range. Process gases and offgases
comprising nitrogen oxide are obtained in these processes and the
nitrogen oxides can be removed inexpensively by means of the
process described here.
[0078] The present invention therefore preferably relates to the
use according to the invention in nitric acid production, in adipic
acid production, for power station offgases, for gas turbines or
for automobile catalysts in the low-temperature range, particularly
preferably in nitric acid production.
[0079] The present invention also provides a process for reducing
the content of nitrogen oxides in a gas by bringing the gas into
contact with a zeolite catalyst as defined above.
[0080] In a preferred embodiment, gases to be treated according to
the invention comprise nitrogen oxides selected from the group
consisting of dinitrogen monoxide N.sub.2O, nitrogen oxides
NO.sub.x, where x is 1 or 2, and mixtures thereof. In a preferred
embodiment, the gas to be treated contains little
(NO.sub.x/N.sub.2O<0.5) and in particular no nitrogen oxides
NO.sub.x. Therefore, a stage for removal of NO.sub.x is inserted
upstream in a preferred embodiment of the process of the invention.
Processes for removal of NO.sub.x are known to those skilled in the
art.
[0081] Particular preference is given to the nitrogen oxide
N.sub.2O being catalytically degraded by means of the process of
the invention so that there is overall a reduction in the content
of this gas in the gas to be treated.
[0082] The gas to be treated according to the invention has a
content of dinitrogen monoxide N.sub.2O of, for example, from 10
ppm by volume to 20% by volume, preferably from 200 ppm by volume
to 10% by volume, particularly preferably from 500 to 2000 ppm by
volume.
[0083] There is no restriction with regard to the further
components present in the gas to be treated. Routine and therefore
preferred further components comprised in the gas to be treated
according to the invention are selected from the group consisting
of water, oxygen, NO, NO.sub.2, NH.sub.3 and N.sub.2 and mixtures
thereof.
[0084] In general, the temperature at which the gas to be treated
is brought into contact with the zeolite catalyst in the reaction
zone is less than 500.degree. C., preferably less than 400.degree.
C., very particularly preferably from 250 to 400.degree. C.
[0085] The present invention therefore preferably provides the
process of the invention carried out at a temperature of less than
400.degree. C., very particularly preferably from 250 to
400.degree. C.
[0086] In a further embodiment, various zeolite catalysts to be
used according to the invention or one or more zeolite catalysts to
be used according to the invention in combination with further
catalysts known to those skilled in the art can be used. When a
plurality of different zeolite catalysts and optionally other
catalysts are used, these can be mixed with one another or be
arranged in succession in the reactor. The latter arrangement is
particularly advantageous when the zeolite catalyst arranged at the
inlet end catalyzes particularly NO.sub.x decomposition, optionally
in the presence of nitrogen-comprising reducing agents, and/or the
zeolite catalyst arranged at the outlet end catalyzes particularly
the decomposition of N.sub.2O.
[0087] Particular preference is given to using a uniform
above-described zeolite catalyst in the process of the
invention.
[0088] The reaction zone can, for the purposes of the present
invention, in principle be configured in any desired way. It can be
present, for example, in a tube reactor or radial basket
reactor.
[0089] The gas laden with nitrogen oxides is usually passed over
the catalyst at a space velocity of from 200 to 200 000 h.sup.-1,
preferably from 5000 to 50 000 h.sup.-1, particularly preferably
from 10 000 to 30 000 h.sup.-1, based on the catalyst volume. For
the present purposes, the term space velocity refers to the ratio
of the volume of gas mixture under STP per hour to the volume of
catalyst. The space velocity can thus be adjusted via the flow
velocity of the gas and/or via the amount of catalyst.
[0090] The process of the invention is preferably carried out at a
GHSV (gas hourly space velocity) of from 2000 to 200 000 standard
l.sub.gas/l.sub.cath (standard I: standard liters-gas volume at
STP), particularly preferably from 5000 to 50 000 standard
l.sub.gas/l.sub.cath very particularly preferably from 10 000 to 30
000 standard l.sub.gas/l.sub.cath.
[0091] The present invention therefore provides, in particular, the
process of the invention in which the GHSV (gas hourly space
velocity) is from 2000 to 200 000 standard l.sub.gas/l.sub.cath
(standard I: standard liters-gas volume at SIP), particularly
preferably from 5000 to 50 000 standard l.sub.gas/l.sub.cath, very
particularly preferably from 10 000 to 30 000 standard
l.sub.gas/l.sub.cath.
[0092] The process of the invention is generally carried out at a
pressure in the range from 1 to 50 bar (a), preferably from 2 to 15
bar (a).
[0093] The process of the invention can, in one embodiment, be
carried out in the presence of at least one reducing agent.
According to the invention, all reducing agents which are able,
under the conditions of the process, to reduce the dinitrogen
monoxide N.sub.2O which is preferably to be degraded are
suitable.
[0094] The present invention therefore preferably provides the
process of the invention in which at least one reducing agent is
additionally used.
[0095] Preferred reducing agents are selected from the group
consisting of nitrogen compounds, for example NH.sub.3,
hydrocarbons, for example methane CH.sub.4 or propane
C.sub.3H.sub.8, CO, SO.sub.2, H.sub.2 and mixtures thereof.
Particularly preferred reducing agents are selected from the group
consisting of NH.sub.3, methane CH.sub.4, propane C.sub.3H.sub.8,
H.sub.2 and mixtures thereof.
[0096] The present invention therefore preferably provides the
process of the invention in which the reducing agent is selected
from the group consisting of nitrogen compounds, hydrocarbons, CO,
SO.sub.2, H.sub.2 and mixtures thereof.
[0097] Apart from NH.sub.3, further suitable nitrogen compounds
are, for example, azanes, hydroxyl derivatives of azanes, and also
amines, oximes, carbamates, urea or urea derivatives.
[0098] An example of an azane is hydrazine.
[0099] An example of hydroxyl derivatives of azanes is
hydroxylamine.
[0100] Examples of amines are primary aliphatic amines such as
methylamine.
[0101] An example of a carbamate is ammonium carbamate.
[0102] Examples of urea derivatives are N,N'-substituted ureas such
as N,N'-dimethylurea. Ureas and urea derivatives are preferably
used in the form of aqueous solutions.
[0103] The way in which the preferably gaseous reducing agent is
introduced into the gas stream to be treated can be chosen freely
for the purposes of the invention; the reducing agent is preferably
introduced upstream (in the flow direction) of the reaction zone.
It can also be introduced, for example, into the inlet line
upstream of the vessel before the catalyst bed or directly before
the bed. The reducing agents can be introduced in the form of gases
or in the form of a liquid or aqueous solution which vaporizes in
the gas stream to be treated. The introduction of any reducing
agent added into the gas to be treated is preferably carried out by
means of a suitable device such as an appropriate pressure valve or
appropriately configured nozzles.
[0104] The amount of any reducing agent added is generally
determined so that, based on the nitrogen oxide to be degraded, an
approximately equimolar amount of reducing agent is present in the
reactor.
[0105] The oxygen content of the reaction gas is preferably less
than 10% by volume, in particular less than 5% by volume.
[0106] The water content of the reaction gas is preferably less
than 10% by volume, in particular less than 1% by volume.
[0107] In general, preference is given to a relatively low water
concentration since higher water contents would make higher
operating temperatures necessary. This could, depending on the
zeolite type used and the time of operation, exceed the
hydrothermal stability limits of the catalyst and therefore has to
be matched to the individual case chosen.
[0108] The content of nitrogen oxides in the gas stream to be
treated can be significantly reduced by the process of the
invention. For example, from 10 ppm by volume to 20% by volume,
preferably from 200 ppm by volume to 10% by volume, particularly
preferably from 500 to 2000 ppm by volume, of the nitrogen oxides,
in particular dinitrogen monoxide N.sub.2O, present at the
beginning are degraded by the process of the invention using the
specific above-described zeolite catalyst.
[0109] According to the invention, the nitrogen oxides present are
catalytically degraded by, preferably, being converted into
nitrogen N.sub.2 and oxygen O.sub.2, in the presence of a reducing
agent additionally into the oxidation product of this reducing
agent, e.g. in the case of H.sub.2 into H.sub.2O.
[0110] The process of the invention can be used, in particular, in
nitric acid production, in adipic acid production, for power
station offgases, for gas turbines or for automobile catalysts in
the low-temperature range. In these processes, process gases and
offgases comprising nitrogen oxide are obtained and can be
inexpensively freed of nitrogen oxides by means of the process
indicated here.
EXAMPLES
1. Catalyst Preparation
[0111] Commercially available zeolites in the H form as powder are
used as starting materials for the catalyst preparation. BEA.sub.10
is the sales product PB/H from Zeochem and MFl.sub.17 corresponds
to PZ 2/25H from the same company. FAU.sub.40 alias CBV 780,
FER.sub.10 alias CP 914C, BEA.sub.140 alias CBV 28014 and
MFl.sub.15 alias CBV 3020E can be purchased from Zeochem.
BEA.sub.140 is treated at 450.degree. C. in a hydrogen atmosphere
for 4 hours before transition metal and phosphorus and/or sulfur
atoms are introduced. This process improves the crystallinity and
acidity of the zeolite.
[0112] All catalysts are firstly impregnated with iron nitrate
solution according to the water uptake of the zeolite. The amount
of solution is thus selected so that the solution is completely
absorbed by the catalyst and is uniformly distributed in the
latter. The amount of iron nitrate is selected so that, after
calcination at 550.degree. C. for 4 hours under a nitrogen
atmosphere, the indicated amount of iron is comprised in the
product. The phosphorus and sulfur contents specified are
subsequently obtained by impregnation (according to the water
uptake) with appropriately diluted phosphoric or sulfuric acid and
renewed calcination under the conditions indicated above. The
powders obtained in this way are subsequently compacted without
washing or similar process steps and crushed. A fraction having
particle sizes from 0.4 to 0.7 mm obtained by sieving is used in
the subsequent testing.
2. Testing
[0113] The catalyst obtained in this way is installed and tested in
a tube reactor. The amount of catalyst corresponds in each case to
0.5 ml. The experiments are carried out at 1.5 bar (a) and a GHSV
(gas hourly space velocity) of 8000 standard l.sub.gas/l.sub.cath.
Gas entering the reactor and gas leaving the reactor are analyzed
to determine the nitrous oxide content by GC analysis (flame
ionization detector) in order to be able to calculate the depletion
or the conversion.
[0114] The mixture of 1000 ppm by volume of N.sub.2O, 3% by volume
of O.sub.2, 0.3% by volume of H.sub.2O and the balance to 100% by
volume of N.sub.2 will hereinafter be referred to as base gas. In
this mixture, part of the nitrogen is optionally replaced by
further components, as follows: 1000 ppm by volume of NO.sub.x
(equilibrium composition of NO and NO.sub.2), 2000 ppm by volume of
H.sub.2, 2000 ppm by volume of NH.sub.3 and/or 500 or 2000 ppm by
volume of C.sub.3H.sub.3. These optional additions are in each case
indicated in the table for the experiment, with the factors 0.5, 1
and 2 before the addition referring to the amount introduced in
1000 ppm by volume increments.
[0115] The results of the individual experiments are shown in
tables 1 and 2. The conversion of N.sub.2O in the base gas at 300
and 400.degree. C. is reported. In the description of the catalysts
used, the subscripts indicate the amount of transition metal or S
and/or P present in percent by weight; the amount of zeolite is not
indicated since the sum of zeolite, transition metal, S and/or P is
in each case 100% by weight. For example, the catalyst
Fe.sub.2.5P.sub.0.4-BEA.sub.140 consists of 2.5% by weight of Fe,
0.4% by weight of P and balance to 100% by weight, i.e. 97.1% by
weight, of zeolite BEA.sub.140. "-" means "not determined".
[0116] The catalysts denoted by "C" in tables 1 and 2 are
comparative examples.
TABLE-US-00001 TABLE 1 Conversion of N.sub.2O at 300.degree. C. in
the base gas +NO.sub.x +NO.sub.x + +2.cndot.H.sub.2 No. Catalyst
pure +NO.sub.x +2.cndot.H.sub.2 2.cndot.C.sub.2H.sub.6
+2.cndot.H.sub.2 +2.cndot.C.sub.2H.sub.6 +0.5.cndot.C.sub.2H.sub.6
+2.cndot.NH.sub.3 no O.sub.2 C1 Fe.sub.2.5-BEA.sub.10 -- 0% -- 12%
-- 100% 84% 53% 67% 2 Fe.sub.2.5P.sub.0.4-BEA.sub.10 -- 12% 27% 34%
100% 100% 60% 100% C3 Fe.sub.2.5-BEA.sub.140 -- -- -- -- -- -- --
-- 96% 4 Fe.sub.2.5P.sub.0.4-BEA.sub.140 -- -- -- -- -- -- -- --
100% C5 Cu.sub.2.5-FAU.sub.40 -- -- -- -- -- -- -- -- 10% 6
Cu.sub.2.5P.sub.2.2-FAU.sub.40 -- -- -- -- -- -- -- -- 17% C7
Fe.sub.2.5-FER.sub.10 0% 5% 7% 10% 7% 9% -- 14% 89% 8
Fe.sub.2.5S.sub.2.1-FER.sub.10 2% -- 7% 11% 18% 12% -- 17% 100% 9
Fe.sub.2.5P.sub.0.4-FER.sub.10 0% 6% 7% 12% 24% 14% -- 32% 100% 10
Fe.sub.2.5P.sub.0.7-FER.sub.10 5% 5% 8% 12% 19% 19% -- 30% 100% 11
Fe.sub.2.5P.sub.1.4-FER.sub.10 0% 4% 1% 6% 14% 31% -- 16% 78% 12
Fe.sub.2.5P.sub.2.2-FER.sub.10 -- -- -- -- -- -- -- -- 65% 13
Fe.sub.2.5P.sub.2.9-FER.sub.10 0% 3% 0% 5% 8% 18% -- 12% 27% 14
Fe.sub.2.5P.sub.3.6-FER.sub.10 -- -- -- -- -- -- -- -- 17% C15
Fe.sub.2.5-MFI.sub.17 0% 0% 0% 12% 0% 91% -- 14% n.d. 16
Fe.sub.2.5P.sub.0.4-MFI.sub.17 1% 2% 0% 16% 8% 90% -- 28% n.d. 17
Fe.sub.2.5P.sub.0.7-MFI.sub.17 2% 4% 13% 15% 8% 81% -- 27% n.d. 18
Fe.sub.2.5P.sub.1.1-MFI.sub.17 0% 3% 0% 15% 19% 88% -- 26% n.d. 19
Fe.sub.2.5P.sub.1.4-MFI.sub.17 0% 4% 0% 14% 7% 92% -- 26% n.d.
TABLE-US-00002 TABLE 2 Conversion of N.sub.2O at 400.degree. C. in
the base gas +NO.sub.x +NO.sub.x +2.cndot.H.sub.2 No. Catalyst pure
+NO.sub.x +2.cndot.H.sub.2 +2.cndot.C.sub.2H.sub.6 +2.cndot.H.sub.2
+2.cndot.C.sub.2H.sub.6 +2.cndot.NH.sub.3 no O.sub.2 C20
Fe.sub.2.5-BEA.sub.10 -- 78% -- -- 35% 100% -- 100% 21
Fe.sub.2.5P.sub.0.4-BEA.sub.10 -- 82% -- -- 48% 100% 69% 100% C22
Cu.sub.2.5-BEA.sub.10 -- -- -- -- 12% -- -- -- 23
Cu.sub.2.5P.sub.0.2-BEA.sub.10 -- -- -- -- 14% -- -- -- 24
Cu.sub.2.5P.sub.0.4-BEA.sub.10 -- -- -- -- 16% -- -- -- 25
Cu.sub.2.5P.sub.0.8-BEA.sub.10 -- -- -- -- 12% -- -- -- 26
Cu.sub.2.5P.sub.1.2-BEA.sub.10 -- -- -- -- 13% -- -- -- 27
Cu.sub.2.5P.sub.1.6-BEA.sub.10 -- -- -- -- 12% -- -- -- C28
Fe.sub.2.5-FAU.sub.40 -- -- -- -- -- -- -- 77% 29
Fe.sub.2.5P.sub.2.2-FAU.sub.40 -- -- -- -- -- -- -- 100% C30
Fe.sub.2.5-FER.sub.10 2% 34% 49% 62% 23% 85% 22% 100% 31
Fe.sub.2.5P.sub.0.4-FER.sub.10 2% 73% 78% 89% 39% 100% 34% 100% 32
Fe.sub.2.5P.sub.0.7-FER.sub.10 9% 74% 79% 80% 53% 100% 55% 100% 33
Fe.sub.2.5P.sub.1.4-FER.sub.10 2% 49% 62% 50% 42% 95% 24% 100% 34
Fe.sub.2.5P.sub.2.2-FER.sub.10 -- 44% 59% -- -- -- -- 100% 35
Fe.sub.2.5P.sub.2.9-FER.sub.10 1% 28% 37% 40% 38% 81% 20% 76% 36
Fe.sub.2.5P.sub.3.6-FER.sub.10 -- 23% 38% -- -- -- -- 73% C37
Fe.sub.2.5-MFI.sub.15 -- -- -- -- -- -- -- 69% 38
Fe.sub.2.5P.sub.2.2-MFI.sub.15 -- -- -- -- -- -- -- 74% C39
Fe.sub.2.5-MFI.sub.17 1% 25% 32% 68% 20% 100% 50% -- 40
Fe.sub.2.5P.sub.0.4-MFI.sub.17 1% 34% 44% 64% 29% 100% 54% -- 41
Fe.sub.2.5P.sub.0.7-MFI.sub.17 1% 34% 29% 63% 26% 100% 37% -- 42
Fe.sub.2.5P.sub.1.1-MFI.sub.17 2% 29% 35% 74% 28% 100% 47% -- 43
Fe.sub.2.5P.sub.1.4-MFI.sub.17 2% 33% 40% 69% 19% 100% 49% -- C44
Cu.sub.2.5-MFI.sub.17 -- -- 0% -- 9% -- -- -- 45
Cu.sub.2.5P.sub.0.2-MFI.sub.17 -- -- 8% -- 14% -- -- -- 46
Cu.sub.2.5P.sub.0.4-MFI.sub.17 -- -- 8% -- 16% -- -- -- 47
Cu.sub.2.5P.sub.0.8-MFI.sub.17 -- -- 8% -- 20% -- -- -- 48
Cu.sub.2.5P.sub.1.2-MFI.sub.17 -- -- 9% -- 18% -- -- -- 49
Cu.sub.2.5P.sub.1.4-MFI.sub.17 -- -- 9% -- -- -- -- -- 50
Cu.sub.2.5P.sub.2.2-MFI.sub.17 -- -- 9% -- -- -- -- -- 51
Cu.sub.2.5P.sub.4.1-MFI.sub.17 -- -- 8% -- -- -- -- --
* * * * *